Autism is a lifelong disorder of unknown origin. The disorder is characterized by behavioural, developmental, neuropathological, and sensory abnormalities (American Psychiatric Association 1994) and is usually diagnosed between the ages of 3 and 10 with peak prevalence rates observed in children aged 5-8 (Yeargin-Allsopp, Rice et al. 2003). At this time, decreased cerebellar Purkinje cell density (Courchesne 1997; Palmen, van Engeland et al. 2004), increased oxidative stress (Yorbik, Sayal et al. 2002; Sogut, Zoroglu et al. 2003; Chauhan, Chauhan et al. 2004; James, Cutler et al. 2004; Zoroglu, Armutcu et al. 2004; Chauhan and Chauhan 2006), and abnormal methionine/homocysteine metabolism (James, Cutler et al. 2004) are the only robust biological characteristics of autism.
Although there is debate as to whether autism has a pre- (Courchesne, Redcay et al. 2004) or post-natal origin (Kern and Jones 2006), it is generally accepted that the symptoms and pathology persist throughout the life of the subject (Bauman and Kemper 2005). These findings suggest that there is an underlying and ongoing biochemical abnormality in autism, regardless of its origin. However, no such underlying biochemical abnormalities have been reported that correlate with the etiology or symptomology of ASD. As such, there is no biochemical test for autism.
Accordingly there is a need for methods that can diagnose ASD in subjects suspected of having ASD or methods that can identify subjects that are at risk of ASD and furthermore there is a need for methods that can assist in the monitoring of therapeutic strategies for the treatment of ASD.